The invention relates to a disc brake, particularly for commercial vehicles, having a caliper straddling a brake disc, an electromechanically or pneumatically operable application device arranged in the caliper for applying the brake, and at least one adjusting device with an electric-motor drive for compensating brake pad wear by adjusting the release play of the disc brake. In particular, the disc brake has at least one electric-motor-driven adjusting rotating device on each side of the brake disc, each of which act by way of at least one pressure piece upon a respective brake pad on each side of the brake disc.
Disc brakes with adjusting systems operated by an electric motor are known per se; such as, for example, from German Patent documents DE 197 56 519 A1 and DE 37 16 202 A1 or International Patent document WO 99/05428.
The use of an electric adjusting motor for driving the adjusting device of the disc brake has been successful per se. In comparison to normal mechanical wear adjusting systems, disc brakes with an electromechanical adjusting device have the advantage that an unacceptably reduced release play (for example, as a result of a thermal expansion of the brake pads) can be augmented again by rotating back the adjusting rotating devices.
In the event of a servicing, the adjusting rotating devices can advantageously be returned automatically into their initial position by means of the electronic control of the adjusting device, thus allowing for the replacement of the worn-out brake pads with new ones.
However, this basic advantage of the electromechanical wear adjusting systems has the problem that it must be designed to preclude the initiation of an unacceptably large resetting as a result of an error in the hardware or software of the electronic control system or by an external influence on the latter.
Although, because of a correspondingly error-tolerant construction of the electronic control system and of the pertaining software, the occurrence of this error can be considered to be virtually excluded, additional protection measures are required because of the serious consequences of this error in the event of any, however improbable, occurrence.
It is therefore an object of the invention to further develop the disc brake of the above-mentioned type such that an unacceptably large reversed rotation of the adjusting rotating devices is reliably prevented.
The invention achieves this task by providing a mechanical device for blocking the electric-motor-driven adjusting setting devices with respect to an augmentation of the release play by the electric-motor drive which exceeds a limit value.
Advantageous further developments are described and claimed herein.
According to the invention, the disc brake has a mechanically operating device that blocks the electric-motor-driven adjusting devices—for example, adjusting rotating devices or drives—with respect to a threshold-exceeding augmentation (increase) of the release play by the electric-motor drive. Completely independent of operations in the electronic system (such as an ABS or EBS control unit of the brake), it therefore becomes possible that, during the normal operation of the brake, a reversed rotation, for example, of the adjusting rotating devices beyond a certain permissible amount is prevented by a mechanical blocking of the adjusting devices.
This invention is particularly suitable for a disc brake, in which at least one adjusting device, respectively, is arranged on each side of the brake disc so that, for compensating brake pad wear, the brake pads on both sides of the brake disc can be adjusted. In this case, the adjusting device(s) can each have at least one or two adjusting rotating device(s).
The blocking forces of the blocking device are preferably proportioned to be at least large enough so that the electric motor drive, or the drives of the adjusting device, cannot overcome the blocking forces and are maintained immobile with respect to the maximal driving torque. As a result, an unintended augmentation of the release play is reliably avoided.
During servicing, the blocking of the adjusting devices is temporarily canceled in order to permit the setting-back of the screws to allow for the exchanging of the brake pads.
The mechanical blockage of the reversed rotation can occur at the driving motors themselves, in the adjusting gearing, or at the adjusting rotating devices.
The blocking by way of the adjusting rotating devices is particularly advantageously achieved in that the adjusting rotating devices are connected with the brake pads for transmitting pull-back forces, and the brake pads are mutually coupled such that, although they can be moved toward one another by the adjusting system in the event of the occurrence of wear, a mutual moving-apart of the brake pads is permitted only to a predefined extent.
In a supplementary fashion, an electronically acting device can be provided for blocking the electric-motor-driven adjusting setting device(s) with respect to an unintentional augmentation of the release play by the electric-motor drive—for example, designed as a corresponding controlling and/or regulating process for controlling the adjusting devices—so that the mechanical blocking device only represents a fall-back (fail-safe) device in the event of a failure of the electronic blocking device.
The mechanical blocking device can be implemented in an uncomplicated manner in various fashions.
The mechanical device for blocking the electric-motor-driven adjusting device is preferably implemented by a mechanical reversed-rotation blocking at the electric-motor drive, particularly at a driving motor, on a gearing, or on the adjusting rotating devices. In this case, it is particularly contemplated to construct the reversed-rotation blocking on the adjusting rotating devices.
In an embodiment, a free wheel is arranged on a shaft end of the respective driving motor, which free wheel permits a rotating movement of the driving motor in the application direction of the adjusting rotating device, but has a blocking effect in the reversed-rotation direction.
In order to permit a slight reversing of the adjusting rotating devices, according to a variant, the housing of the free wheel can be connected with an elastic element, such as a flat coil spring. In this manner, when the motor shaft is moved by a reversed rotation, the flat coil spring is first wound up by way of, optionally, several rotations before a further rotation of the motor shaft is prevented by means of the free wheel and the pretensioned flat coil spring acting upon the latter. The outer end of the flat coil spring is connected with the caliper and can be uncoupled therefrom. For changing the brake pads, the fixing of the outer end of the flat coil spring can be released by a manual operation, so that a reversed rotation of the adjusting rotating devices is permitted.
Instead of using the flat coil spring, a limited reversing can also be achieved by combining a free wheel with a screwing element. In this case, the housing of the free wheel is axially displaceably but non-rotatably accommodated in a sleeve which has an external thread on its outside diameter, with which external thread, it engages with an internal thread in the caliper.
When the free wheel now locks during a reversed-rotating movement of the engine shaft, the free wheel rotates the outer sleeve into the internal thread receiving it and, in the process, moves this sleeve in the axial direction by way of, optionally, several rotations against a stop. When the stop has been reached, a further rotating movement is prevented.
The two above-described reversed-rotation securing mechanisms, as well as contemplated equivalent embodiments thereof, in the same manner as on the motor shaft, can be arranged on each shaft of the adjusting gearing connected on the output side. Corresponding to the ratio to the shaft of the driving motor, a smaller angle of rotation is required while the adjusting forces are correspondingly larger.
In a further preferred manner, the pressure pieces are connected with pad holding plates.
This solution utilizes the fact that the adjusting pistons for achieving an active release of the brake pads after the braking operation are mechanically coupled with the respectively acted-upon brake pad in the sense of a transmission of a reversing movement. This mechanical coupling can take place in a form-locking manner (for example, mutually engaging profiles of the pressure element and of the back of the brake pad), in a material-locking manner (gluing, welding, etc.) or in a force-locking manner (for example, by way of clamp springs).
If the two brake pads are now mutually connected by way of a second coupling device such that, although they can be moved toward one another for the purpose of the wear adjustment, a moving-apart is prevented starting from a predefined amount in the second coupling device, the adjusting rotating devices of the internal as well as of the external adjusting device are thereby blocked.
As mentioned above, a blocking of the screws can be implemented by way of coupled brake pads. In a particularly preferred manner, the two brake pads are coupled with one another in a constructively simpler and more cost-effective fashion such that, for the purpose of the wear adjustment, they can be moved toward one another but can be moved away from one another only by not more than a small predefined amount. In this manner, the brake pads are mutually coupled such that, although in the event of an occurrence of wear, the brake pads can be moved toward one another by means of the adjusting device on both sides of the brake disc, a moving-apart of the brake pads is permitted only by way of a predefined path.
The brake pad holding device oftentimes consists of a brake pad holding clamp which extends at a right angle with respect to the friction surfaces of the brake disc beyond the latter and the brake pads and is supported at both ends on the caliper. The brake pad holding clamp presses the two brake pads by way of the brake pad holding springs placed upon these brake pads against the supporting surfaces in the brake pad guide of the caliper. The coupling device can therefore be constructed on a brake pad holding clamp, which extends at a right angle with respect to the friction surfaces of the brake disc beyond the latter and the brake pads and is supported at both ends on the caliper. The brake pad holding clamp presses the two brake pads by way of the brake pad holding spring placed upon the latter against the supporting surfaces in the brake pad guide of the caliper. In this manner, a particularly secure blocking device is implemented in a particularly cost-effective fashion.
The brake pad holding clamp is, preferably, axially moveably accommodated in abutments at the caliper, and/or, on its surface facing the brake pads is equipped with a profiling, particularly with a saw-toothed profile, in the areas in which the brake pad holding springs are supported against the brake pad holding clamp. The additional costs of the construction as a result of the construction of the blocking device are kept particularly low in this manner while the operating reliability is excellent.
The profiling preferably has two profiling sections oriented in opposite directions, so that a displacing of the brake pads in the direction of the brake disc can take place with relatively little force, whereas a moving-away of the brake pads from the brake disc can be implemented only by means of a greater force as a result of the profilings.
Projections engaging in the profiling are preferably constructed on the brake pad holding springs, and the brake pad holding springs are received with an axial play on the brake pads.
In another embodiment of the invention, the brake pad holding clamp is axially movably received in its abutments at the caliper; for example, with an axial displaceability of approximately 2 mm. By means of a controlling of the internal and external adjusting devices in opposite directions, it becomes possible in this manner to push the entire unit consisting of the brake disc and brake pad holding clamp/brake pad set back and forth in this area without changing the total release play and the claw-type connection between the brake pad holding clamp and the brake pad holding springs.
It is also contemplated that the profiled sections are arranged in a component that is itself arranged between the brake pad holding clamp and the brake pad holding springs. The component is displaceable relative to the brake pad holding clamp.
This function is important in the case of fixed-caliper brakes with an external wear adjustment and a micro-displaceable brake disc.
Embodiments of the invention are also contemplated in which the second coupling device is constructed to be separate, that is, not combined with the brake pad holding device. For example, the brake pads can be coupled by way of a cylinder-piston element, in which case the cylinder (or the two cylinders) is fastened to the first brake pad, and the piston (or the two pistons) is fastened to the brake pad which is, in each case, situated opposite the brake disc. Here, the piston end can be equipped with elastic projections which engage in corresponding profilings, such as circling sawtooth grooves in the internal cylinder surfaces.
However, preferably a continuously operating reversed-rotation securing mechanism can also be created by means of the cylinder-piston combination. This can be implemented by means of clamping mechanisms which, in principle, operate similarly to the described mechanical locking. However, preferably, a free wheel is arranged on the pin-shaped end of the piston, which free wheel carries a non-self-locking thread on its enveloping housing, which thread engages in a complementary internal thread in the cylinder. The free wheel is accommodated in a secured manner on the piston pin for transmitting axial forces. The locking direction of the free wheel is selected such that the brake pads can be moved toward one another at a relatively low expenditure of force. However, the free wheel locks when the brake pads are moving apart, so that no relative movement takes place in the thread. A slight reverse movement is permitted by a play in the thread or in the axial securing of the free wheel.
Advantageous further developments of the invention are described and claimed herein.
In the following, the invention will be explained in detail with reference to the attached figures.